At Anglo American Platinum's Precious Metal Refinery, rhodium separates from a base metal-rich solution by precipitation. Hexachlororhodate (III) ions and cationic protonated diethylenetriamine ions exchange to form diethylenetriammonium hexachlororhodate (III) crystals, a rhodium metal precursor. The objective of this work is to determine nucleation and growth kinetics of diethylenetriammonium hexachlororhodate (III) salt. Two reactor configurations, namely a transient continuous stirred tank reactor (CSTR) and a t-mixer plug flow reactor (PFR), were used to determine nucleation and growth rates. The objective of the configurations was to eliminate kinetic biases that may be caused by mixing at the mesoscale. Transient saturation in the CSTR ranged up to 43, and in the PFR saturation was varied between 2 and 64. Precipitation kinetic parameters were estimated through data fitting concentration and volume average crystal size profiles to a mass and population balance model. Temperature dependence of kinetic parameters was found to be universal between reactor configurations. Both growth through interfacial attachment and agglomeration, as defined in this work, were exothermic processes with activation energies of -192.9kJ/mol and -656.1kJ/mol respectively. Nucleation was found to be an endothermic process with an activation energy of 50.9kJ/mol in accord with the observed heat of crystallisation. No evidence of heterogeneous primary nucleation in the form of crystals adhering to the side walls of the reactor or the agitator blades was observed. The experiments were not explicitly designed to distinguish between primary and secondary nucleation mechanisms, therefore excluding one over the other is not justified. However, considering the presence of nucleated crystals in each system combined with the good model fit using a nucleation rate expression typically associated with secondary nucleation, it is likely that the dominating nucleation mechanism is secondary in nature. In the PFR configuration, nucleation and growth occur at a faster rate compared to the CSTR under the experimental conditions in this work. This observation is inferred from the fitted temperature independent kinetic parameters and is linked to a much higher mixing intensity achieved in the PFR relative to the CSTR. Flow conditions, described by the Reynolds number, can limit conversion in the PFR configuration by a mixing limitation at the micro- or mesoscale. Micro- and mesoscale mixing were represented by a characteristic length scale that was empirically related to temperature for the microscale and fluid velocity for the mesoscale. Under conditions where the Reynolds number is below the point where conversion is independent of the Reynolds number, either micromixing or mesomixing can become a rate limitation. At a sufficiently high Reynolds number neither micromixing nor mesomixing limits conversion and the system equilibrium becomes the limitation. In the CSTR, the system equilibrium limited reaction conversion as the micro- and mesoscale mixing zones were sufficiently small relative to the reactor volume. Parameters related to mixing were found to differ between the configurations, which was caused by different flow patterns within each configuration. Scanning electron microscopy (SEM) photographs suggest that crystals in the PFR configuration collide both in the radial and axial direction, giving rise to a feathery flat and elongated agglomerated crystal cluster. In contrast, the crystals in the CSTR configuration collide in a chaotic but consistent pattern, giving rise to a desert rose-like agglomerated crystal cluster. The derived model used to describe agglomeration is based on the agglomeration principles proposed by Von Smoluchowski coupled with Fick's law of diffusion and gives a good representation of crystal size. The PFR growth rate supersaturation exponent was 1.13, suggesting a Burton-Cabrera-Frank type growth model, and is indicative of crystal growth from screw dislocations that is limited either through mass transfer to the crystal surface, or surface integration. Thus, in this instance, the rate of aqueous hexachlororhodate (III) conversion to crystal would be responsive to mixing conditions on the micro- or mesoscale, as was experimentally found in the PFR configuration. In comparison, the CSTR growth rate supersaturation exponent was 2.31 and is more in line with polynuclear growth that appears to be limited by interfacial attachment kinetics, as the system equilibrates in the bulk. Lastly, a key finding of this work is the ability to manipulate the crystal morphology by changing reactor configuration. By creating elongated flat crystal structures in the PFR configuration as opposed to a desert rose crystal structure in the CSTR, it may be possible to reduce impurities within the crystal by entraining less mother liquor.

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No. of bitstreams: 1 DissMMJ.pdf: 1828985 bytes, checksum: 46683e867b5c537c6e708b4cc9f3c4df (MD5) Previous issue date: 2015-04-24 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Brazil is the largest producer of cane sugar and the largest producer and exporter of sugar being the state of São Paulo the responsible for over 60% of the national production of sugar, and the region is where is located the city of São Carlos is main producer region of Brazil, this fact becomes a motivation for this project. The crystallization process is the most important in the production of sugar and responsible for the quality of the final product. This work deals with the modeling and simulation of this process through three different approaches: the ideal crystallizer (MSMPR), the integrated sugar production without description of crystals, approach called "gray-box", and the industrial crystallizer. The models were developed in the software EMSO. The EMSO is a program developed in Brazil and has a great advantage compared to other programs, it's a free program, without the need to license purchase. By allowing full access to the developed mathematical models, facilitates the insertion of new models such as the present study about crystallization and allow the improvement of existing models, allowing also the development of specific software libraries. The first held approach, MSMPR, aims to introduce a protocol currents description containing solids and the crystallization process in the EMSO, for in his library there is no model that describes the crystallization or even containing solids, unlike other widely used commercial programs for the simulation of processes such as Aspen Plus, having a model MSMPR. So when performing this first approach, the EMSO can match other programs in relation to the crystallization process. The mass averaged crystal size (MA) obtained with the parameters set as default, L43 = 1.18 mm is much greater than the expected value L43 = 0.5 to 0.55 mm, but with the variation of the kinetic parameters can be obtained results within the desired range . The second approach is a simplified model called "gray-box" in order to facilitate the paying in of crystallization models with models referring to others process. The sugar production obtained in this model was similar than that reported in the literature, but the model can be useful in paying in of process models which constitute a industrial plant. The third and most important approach corresponds to the model of an industrial crystalliser with intent to represent real process of sugar production using data from literature. The discussion was carried out on the variables: temperature, brix, crystal mass and MA. The variations of temperature and brix relative to time obtained are consistent with each step of the process. The crystal mass produced in the simulation is approximately 50% lower than that found in the literature, whereas the MA is also below, but achieves excellent results in the change of the kinetic parameters. The final results obtained in the simulations do not coincide with the expected results, but the easy access to developed models makes these models a good instrument to parameters analysis, reaching with some changes in the kinetic parameters, in satisfactory results that well represent the real process. / O Brasil é o maior produtor mundial de cana-de-açúcar e o maior produtor e exportador de açúcar sendo que o estado de São Paulo é responsável por mais de 60% da produção nacional de açúcar, sendo o interior paulista a principal região produtora do Brasil, tal fato torna-se uma motivação para o presente projeto, pois é onde localiza-se a cidade de São Carlos. A etapa de cristalização é a mais importante na produção de açúcar, por ser a responsável pela qualidade do produto final. O presente trabalho trata da modelagem e simulação desse processo através de três diferentes abordagens: o cristalizador ideal (MSMPR), o processo integrado de produção de açúcar sem descrição dos cristais, abordagem denominada “caixacinza”, e o cristalizador industrial. Os modelos foram desenvolvidos no software EMSO. O EMSO é um programa desenvolvido no Brasil e possui um grande diferencial em relação aos demais programas de ser de uso gratuito, sem a necessidade de compra de licença. Por possibilitar acesso total aos modelos matemáticos desenvolvidos, facilita a inserção de novos modelos, como os de cristalização do presente trabalho e permitem o aprimoramento de modelos já existentes, possibilitando, ainda, o desenvolvimento de bibliotecas específicas no software. A primeira abordagem realizada, o MSMPR, tem como objetivo introduzir um protocolo de descrição de correntes contendo sólidos e o processo de cristalização no EMSO, pois em sua biblioteca não existe nenhum modelo que descreva a cristalização ou até mesmo que contenha sólidos, diferente de outros programas comerciais muito utilizados para a simulação de processos, como o Aspen Plus, que possui um modelo de MSMPR. Então ao realizar essa primeira abordagem o EMSO pode se igualar a outros programas em relação ao processo de cristalização. O tamanho médio mássico obtido com os parâmetros estabelecidos como padrão, L43 = 1,18 mm é muito maior que o valor esperado L43 = 0,5 a 0,55 mm, porém com a variação dos parâmetros cinéticos os resultados obtidos estão na faixa desejada. A segunda abordagem trata de um modelo simplificado denominado “caixa-cinza” com o objetivo de facilitar a integralização da cristalização com modelos referentes a outros processos. A produção de açúcar obtida nesse modelo foi similar à apresentada na literatura, sendo assim, o modelo pode ser útil em uma estimativa de produção do processo e na integralização de modelos de processos que constituem uma usina. A terceira e mais importante abordagem corresponde ao modelo de um cristalizador industrial, com a intenção de representar o processo real na produção de açúcar utilizando dados provenientes da literatura. A discussão dos resultados procedeu-se sobre as variáveis: temperatura, brix, massa de cristais e tamanho médio mássico. As variações da temperatura e do brix em relação ao tempo obtidas condizem com cada etapa do processo. A massa de cristal produzida na simulação é proximadamente 50% menor do que a encontrada na literatura, enquanto que o tamanho médio também está abaixo mas atinge ótimos resultados com a alteração dos parâmetros cinéticos. Os resultados finais obtidos nas simulações não coincidiram com os resultados esperados, porém o fácil acesso aos modelos desenvolvidos torna esses modelos bons instrumentos de análises de parâmetros, podendo chegar com algumas mudanças nos parâmetros cinéticos, a resultados satisfatórios que representem bem o processo real.

Abstract: Sodium bicarbonate is one of the major chemical compound used worldwide. We have studied the mechanisms presiding the crystallization of this product in order to identify the kinetic parameters. To be assured of the relevancy of our experimental results, we developed new and accurate measurement techniques to follow the supersaturation and to characterize the crystal morphologies of NaHCO3 like density measurement and images analysis. The systematic study of the mechanisms and the kinetic parameters of the crystallization of NaHCO3 has been conducted by the use of three different types of crystallizers conceived and built at the Department of Industrial Chemistry of ULB : a fluidized bed crystallizer, a classic MSMPR crystallizer and a bubble column. By this choice, we were able to thoroughly investigate the intrinsic phenomena occurring in the crystallization of NaHCO3 from the ideal condition to the conditions close to the industry. A NaHCO3 solution is typically a three components equilibrium, NaHCO3, Na2CO3 and CO2, depending on temperature. Our developed method of density measurement allows to measure continuously the supersaturation, during the crystallization. This method permits to neglect complex side effects due to Na2CO3 or dissolved mineral impurities. Density measurements are quick, sensitive and reliable. We have shown that the growth of sodium bicarbonate is widely controlled by a reaction step at 45°C (< 200 µm). A diffusion step controlled growth occurs however for large crystals (>300-425µm) which consume much less material than the small ones. We have shown that the secondary nucleation of NaHCO3 is principally dominated by the surface nucleation. The shape of the crystals obtained experimentally is in agreement with the theory, and strongly related to the size of the crystals and to the presence of impurities. Based on experience of NaHCO3 crystallization without introduction of impurity, we have demonstrated that Ca2+ and Mg2+ suppress crystallization kinetics. In the end, we have taken a brief look at the precipitation of NaHCO3 by gaz-liquid reaction in a bubble column. By a comparative and a fundamental approach, our experimental studies lead us to improve our understanding and the operational parameters of the NaHCO3 industrial refining process. Key words: Industrial crystallization, Sodium bicarbonate, Density measurement, Fluidized bed, MSMPR, Bubble column, Crystal growth, Nucleation Résumé: Le bicarbonate de sodium (NaHCO3) est un produit chimique important sur le marché mondial. Nous avons étudier les mécanismes de la cristallisation de ce produit afin d'en déterminer les paramètres cinétiques. Afin de garantir l'analyse la plus objective de ces phénomènes, nous avons développé des techniques de mesures originales pour la connaissance de la sursaturation et pour la caractérisation des cristaux de NaHCO3 par densimétrie et par analyse d’images. L'étude systématique des cinétiques et des mécanismes de cristallisation du NaHCO3 a été réalisée au moyen de trois cristallisoirs de conception différente, développés et construits au laboratoire du Service de Chimie Industrielle de l'ULB: un cristallisoir à lit fluidisé, un cristallisoir à cuve agitée MSMPR et une colonne à bulles. Ce choix nous a permis d'approfondir notre connaissance des phénomènes intrinsèques de la cristallisation du NaHCO3 dans des conditions idéales et des conditions proches des procédés industriels. Une solution de NaHCO3 est un système à l’équilibre à trois composantes, NaHCO3, Na2CO3 et CO2 fonction de la température. La mise au point de la méthode densimétrique a permis la mesure de la sursaturation en NaHCO3 en continu. Cette méthode permet de s’affranchir des complications introduites par la présence de Na2CO3 et des impuretés inorganiques en solution. Les mesures de masse volumique sont rapides, précises et sensibles. Nous avons démontré que la croissance du bicarbonate de sodium est largement dominé par l'étape de réaction à 45°C (< 200 µm). L'étape de diffusion intervient cependant dans la croissance de grands cristaux (>300-425µm) qui ne sont toutefois pas les plus grands consommateurs de matière. Nous avons mis en évidence que le mécanisme de la germination secondaire du NaHCO3 est principalement une germination secondaire vraie. La forme des cristaux obtenus est parfaitement en accord avec la théorie et dépend étroitement de la taille des cristaux mais également de la présence d'impuretés. En se basant sur les expériences de cristallisation du NaHCO3 sans introduction d’impuretés, nous avons démontré les effets de ralentissement des cinétiques de cristallisation d'ions tels que Ca2+ et Mg2+ . Nous avons enfin brièvement abordé la précipitation du NaHCO3 par réaction gaz-liquide dans une colonne à bulles. Cette approche expérimentale, comparative et fondamentale a permis d'affiner notre compréhension et d’optimiser un procédé industriel de raffinage du bicarbonate de sodium. Mots clés: Cristallisation industrielle, Bicarbonate de sodium, Densimétrie, Lit fluidisé, MSMPR, Colonne à bulles, Croissance des cristaux, Germination

In this thesis novel configurations and operating strategies in the mixed suspension mixed product removal (MSMPR) crystalliser are investigated, aided by integrated process analytical technologies (PAT) and crystallisation informatics system (CryPRINS) tools. The MSMPR is an idealised crystalliser model that assumes: steady-state operation; well mixed suspension with no product classification, such that all volume elements contain a mixture of particles (small and large) and crystal size distribution (CSD) that is independent of location in the crystalliser and is identical of the product withdrawn; and uniform supersaturation thought, leading to constant nucleation and growth rates. Single-stage MSMPR designs with continuous recycle/recirculation and modified heat exchanger were investigated and found to minimise fouling, encrustation and transfer line blockages. In particular, a modified MSMPR with baffled heat exchanger was found to significantly reduce the temperature between incoming feed hot feed solution and the cooled crystalliser, leading to a significant reduction in fouling, encrustation and blockages. In addition, the concept of the periodic mixed suspension mixed product removal (PMSMPR) crystallisation process is demonstrated for the first time viz single- and multi-stage cascaded operations. This method of operation involves the periodic transfer of slurry (addition and withdrawal) at high flow rates from either a single stirred vessel or between a number of stirred vessels arranged in series. The PMSMPR is therefore characterised by periodic withdrawals of product slurry. Similar to the MSMPR, the product withdrawn from a PMSMPR has exactly the same composition as the vessel at the time of removal. The rapid withdrawal of slurry at high flow rates in PMSMPR operation leads to the prevention of particle sedimentation and blockage of transfer lines. The transfer of slurry (to/from) the PMSMPR is followed by a holding (or pause) period when no addition or withdrawal of slurry takes place. The holding period extends the mean residence time of the PMSMPR relative to a typical MSMPR, thereby increasing the yield and productivity of crystallisation as more time is allowed for consumption of available supersaturation viz crystal growth and nucleation. A state of controlled operation (SCO) in the periodic flow process, defined as a state of the system that maintains itself despite regular, but controlled disruptions was characterised using the PAT tools and CryPRINS within an intelligent decision support (IDS) framework. The crystallisation of paracetamol (PCM) from isopropyl alcohol (IPA) using different configurations of a single-stage continuous MSMPR crystalliser that incorporated continuous recycle and recirculation loop, and a novel design with baffled heat exchanger was investigated. Crystallisations of PCM-IPA carried out in the MSMPR without heat exchanger suffered from severe fouling, encrustation and blockage problems due to the high level of supersaturation (S = 1.39) in the crystalliser, which was required for the initial burst of nucleation to generate enough particles for later growth, as well as the large temperature difference between the incoming feed (45 oC) and the crystalliser (10 oC). Using the modified MSMPR design with baffled heat exchanger, the challenges of fouling, encrustation and blockage were significantly reduced due to the rapid lowering of the feed stream temperature prior to entering the crystalliser. In addition, the closed loop system led to conservation of material, which is a great benefit since large amounts of materials would otherwise be required if the MSMPR was operated with continuous product removal. This design is great for research purposes, in particular, to investigate process design and optimisation. Continuous crystallisation of PCM in the presence of hydroxyl propyl methyl cellulose (HPMC) additive was investigated in the modified MSMPR design with heat exchanger. HPMC was found to improve the crystallisation performance, leading to complete avoidance of fouling, encrustation and blockages at a concentration of 0.05 wt%. However, the yield of crystallisation was significantly reduced (28.0 %) compared to a control experiment (98.8 %, biased due to fouling/encrustation) performed without additive addition. Regardless, the productivity of crystallisation was more than four times that achieved in batch linear cooling (LC) (0.62 0.86 g/L-min) and batch automated dynamic nucleation control (ADNC) (0.24 0.25 g/L-min) runs. Aspects of the periodic flow crystallisation of single- and multi-component (co-crystals) molecular systems have also been examined to demonstrate the concept of state of controlled operation . The single component systems studied were PCM and glycine (GLY), each representative of compounds with slow and fast growth kinetics, respectively. The co-crystal systems investigated were urea-barbituric acid (UBA) and p Toluenesulfonamide-Triphenylphosphine oxide (p-TSA-TPPO). UBA is a polymorphic co-crystal system with three known forms (I, II and III). Form I UBA was successfully isolated in a three-stage periodic flow PMSMPR crystalliser. This study demonstrates the capability of periodic flow crystallisation for isolation of a desired polymorph from a mixture. p-TSA-TPPO exists in two known stoichiometric co-crystal forms, 1:1 and 3:2 mole ratio p-TSA-TPPO, respectively. The two crystalline forms exhibit solution mediated transformation, which proves to be a difficulty for separation. For this study, the implementation of temperature cycles in batch and flow control in semi-batch and periodic PMSMPR crystallisers were investigated to isolate pure 1:1 and 3:2 p-TSA-TPPO, respectively. Different regions of the ternary diagram of p-TSA, TPPO and acetonitrile (MeCN) were investigated. The desired co-crystal form was isolated all crystallisation platforms investigated. However, greater consistency was observed in the semi-batch and PMSMPR operations respectively. Periodic flow crystallisation in PMSMPR is a promising alternative to conventional continuous MSMPR operation, affording greater degrees of freedom operation, slightly narrower RTD profiles, consistent product crystal quality (size, shape and distribution), longer mean residence times, higher yield and productivity and significant reduction in fouling, encrustation and transfer line blockages over prolonged operating periods. Furthermore, the PMSMPR is a versatile platform that can be used to investigate a range of different molecular systems. Relative to batch operation, the PMSMPR can operate close to equilibrium, however, this is dependent on the system kinetics. In addition, retrofitting of batch crystallisers to operate as PMSMPRS fairly simple and require only subtle changes to the existing design space. The integrated array of PAT sensors consisted of attenuated total reflectance ultra violet/visible spectroscopy (ATR-UV/vis), attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), focused beam reflectance measurement (FBRM), particle vision microscopy (PVM) and Raman spectroscopy. The results from the studies reported here illustrate very well the use of PAT and information system tools together to determine when the continuous and periodic MSMPR operations reaches a steady-state or state of controlled operation (i.e. periodic steady-state). These tools provided a better understanding of the variables and operating procedures that influence the two types of operations.

The purpose of the work described in this thesis was to explore the use of fractional crystallization as a technology that can be used to separate medium-curie waste from the Hanford Site tank farms into a high-curie waste stream, which can be sent to a Waste Treatment and Immobilization Plant (WTP), and a low-curie waste stream, which can be sent to Bulk Vitrification. The successful semi-batch crystallization of sodium salts from two single shell tank simulant solutions (SST Early Feed, SST Late Feed) demonstrated that the recovered crystalline product met the purity requirement for exclusion of cesium, sodium recovery in the crystalline product and the requirement on the sulfate-to-sodium molar ratio in the stream to be diverted to the WTP. The experimental apparatus, procedures and results obtained in this thesis on scaled-down experiments of SST Early and Late Feed simulated solutions were adapted and reproduced under hot-cell with actual wastes by our partners at Hanford. To prepare the application of the pretreatment process to pilot scale process, several varation to the feed solutions were investigated including the presence of carboxylates and amines organics compounds and solids particles. Results of the study showed that 4 organics species presented complications to the process (NTA, HEDTA, EDTA and sodium citrate) while the other species (Formate, acetate, glycolate and IDA) and solids particles did not in the conditions of the stored wastes. In this thesis, the kinetics of the crystalline species formed at the condition of the early feed certification run (66 °C and 25 g/h evaporation) were determined along with the effect of the operating temperature and evaporation rate on these kinetics. On one hand, the study of evaporation rate values ranging from 25g/h to 75g/h showed that an increase in evaporation rate increased the specific nucleation while decreasing the specific growth rate. On the other hand, experiments on operating temperature ranging from 35 °C to 75 °C displayed that the nucleation rate of all species increased with temperature at the exception of sodium carbonate monohydrate and burkeite crystals, and that the growth rate of all species increased with temperature at the exception of sodium nitrate. Furthermore, sulfate based crystals such as trisodium fluoride sulfate were only roduced at 45 °C and 75 °C. A simple steady state MSMPR population balance model was developed expressing the total population density function as the sum of the specific population density functions. The specific semi-batch crystallization kinetics were implemented in this model.

Abstract:<p><p>Sodium bicarbonate is one of the major chemical compound used worldwide. We have studied the mechanisms presiding the crystallization of this product in order to identify the kinetic parameters.<p>To be assured of the relevancy of our experimental results, we developed new and accurate measurement techniques to follow the supersaturation and to characterize the crystal morphologies of NaHCO3 like density measurement and images analysis.<p>The systematic study of the mechanisms and the kinetic parameters of the crystallization of NaHCO3 has been conducted by the use of three different types of crystallizers conceived and built at the Department of Industrial Chemistry of ULB :a fluidized bed crystallizer, a classic MSMPR crystallizer and a bubble column. By this choice, we were able to thoroughly investigate the intrinsic phenomena occurring in the crystallization of NaHCO3 from the ideal condition to the conditions close to the industry. <p>A NaHCO3 solution is typically a three components equilibrium, NaHCO3, Na2CO3 and CO2, depending on temperature. Our developed method of density measurement allows to measure continuously the supersaturation, during the crystallization. This method permits to neglect complex side effects due to Na2CO3 or dissolved mineral impurities. Density measurements are quick, sensitive and reliable.<p>We have shown that the growth of sodium bicarbonate is widely controlled by a reaction step at 45°C (< 200 µm). A diffusion step controlled growth occurs however for large crystals (>300-425µm) which consume much less material than the small ones. We have shown that the secondary nucleation of NaHCO3 is principally dominated by the surface nucleation. <p>The shape of the crystals obtained experimentally is in agreement with the theory, and strongly related to the size of the crystals and to the presence of impurities.<p><p>Based on experience of NaHCO3 crystallization without introduction of impurity, we have demonstrated that Ca2+ and Mg2+ suppress crystallization kinetics.<p>In the end, we have taken a brief look at the precipitation of NaHCO3 by gaz-liquid reaction in a bubble column. <p><p>By a comparative and a fundamental approach, our experimental studies lead us to improve our understanding and the operational parameters of the NaHCO3 industrial refining process.<p><p>Key words: Industrial crystallization, Sodium bicarbonate, Density measurement, Fluidized bed, MSMPR, Bubble column, Crystal growth, Nucleation<p><p>Résumé: <p><p>Le bicarbonate de sodium (NaHCO3) est un produit chimique important sur le marché mondial. Nous avons étudier les mécanismes de la cristallisation de ce produit afin d'en déterminer les paramètres cinétiques. <p>Afin de garantir l'analyse la plus objective de ces phénomènes, nous avons développé des techniques de mesures originales pour la connaissance de la sursaturation et pour la caractérisation des cristaux de NaHCO3 par densimétrie et par analyse d’images. <p>L'étude systématique des cinétiques et des mécanismes de cristallisation du NaHCO3 a été réalisée au moyen de trois cristallisoirs de conception différente, développés et construits au laboratoire du Service de Chimie Industrielle de l'ULB: un cristallisoir à lit fluidisé, un cristallisoir à cuve agitée MSMPR et une colonne à bulles. Ce choix nous a permis d'approfondir notre connaissance des phénomènes intrinsèques de la cristallisation du NaHCO3 dans des conditions idéales et des conditions proches des procédés industriels. <p>Une solution de NaHCO3 est un système à l’équilibre à trois composantes, NaHCO3, Na2CO3 et CO2 fonction de la température. La mise au point de la méthode densimétrique a permis la mesure de la sursaturation en NaHCO3 en continu. Cette méthode permet de s’affranchir des complications introduites par la présence de Na2CO3 et des impuretés inorganiques en solution. Les mesures de masse volumique sont rapides, précises et sensibles.<p>Nous avons démontré que la croissance du bicarbonate de sodium est largement dominé par l'étape de réaction à 45°C (< 200 µm). L'étape de diffusion intervient cependant dans la croissance de grands cristaux (>300-425µm) qui ne sont toutefois pas les plus grands consommateurs de matière. Nous avons mis en évidence que le mécanisme de la germination secondaire du NaHCO3 est principalement une germination secondaire vraie.<p>La forme des cristaux obtenus est parfaitement en accord avec la théorie et dépend étroitement de la taille des cristaux mais également de la présence d'impuretés.<p><p>En se basant sur les expériences de cristallisation du NaHCO3 sans introduction d’impuretés, nous avons démontré les effets de ralentissement des cinétiques de cristallisation d'ions tels que Ca2+ et Mg2+ .<p>Nous avons enfin brièvement abordé la précipitation du NaHCO3 par réaction gaz-liquide dans une colonne à bulles. <p><p>Cette approche expérimentale, comparative et fondamentale a permis d'affiner notre compréhension et d’optimiser un procédé industriel de raffinage du bicarbonate de sodium.<p><p>Mots clés: Cristallisation industrielle, Bicarbonate de sodium, Densimétrie, Lit fluidisé, MSMPR, Colonne à bulles, Croissance des cristaux, Germination <p><p> / Doctorat en sciences appliquées / info:eu-repo/semantics/nonPublished